eqn not supportedXDrawArc draws a single circular
or elliptical arc, and XDrawArcs draws multiple circular or elliptical
arcs. Each arc is specified by a rectangle and two angles. The center of
the circle or ellipse is the center of the rectangle, and the major and
minor axes are specified by the width and height. Positive angles indicate
counterclockwise motion, and negative angles indicate clockwise motion.
If the magnitude of angle2 is greater than 360 degrees, XDrawArc or
XDrawArcs truncates it to 360 degrees.

For an arc specified as %[ ~x,
~y, ~width , ~height, ~angle1, ~angle2 ]%, the origin of the major and
minor axes is at % [ x +^ {width over 2} , ~y +^ {height over 2} ]%, and
the infinitely thin path describing the entire circle or ellipse intersects
the horizontal axis at % [ x, ~y +^ {height over 2} ]% and % [ x +^ width
, ~y +^ { height over 2 }] % and intersects the vertical axis at % [ x +^
{ width over 2 } , ~y ]% and % [ x +^ { width over 2 }, ~y +^ height ]%.
These coordinates can be fractional and so are not truncated to discrete
coordinates. The path should be defined by the ideal mathematical path.
For a wide line with line-width lw, the bounding outlines for filling
are given by the two infinitely thin paths consisting of all points
whose perpendicular distance from the path of the circle/ellipse is equal
to lw/2 (which may be a fractional value). The cap-style and join-style are
applied the same as for a line corresponding to the tangent of the circle/ellipse
at the endpoint.

For an arc specified as % [ ~x, ~y, ~width, ~height, ~angle1,
~angle2 ]%, the angles must be specified in the effectively skewed coordinate
system of the ellipse (for a circle, the angles and coordinate systems
are identical). The relationship between these angles and angles expressed
in the normal coordinate system of the screen (as measured with a protractor)
is as follows:

The skewed-angle and normal-angle are expressed in radians (rather than
in degrees scaled by 64) in the range % [ 0 , ~2 pi ]% and where atan
returns a value in the range % [ - pi over 2 , ~pi over 2 ] % and adjust
is:

For any given arc, XDrawArc and XDrawArcs do not draw a pixel more
than once. If two arcs join correctly and if the line-width is greater
than zero and the arcs intersect, XDrawArc and XDrawArcs do not draw
a pixel more than once. Otherwise, the intersecting pixels of intersecting
arcs are drawn multiple times. Specifying an arc with one endpoint and a
clockwise extent draws the same pixels as specifying the other endpoint
and an equivalent counterclockwise extent, except as it affects joins.

If
the last point in one arc coincides with the first point in the following
arc, the two arcs will join correctly. If the first point in the first
arc coincides with the last point in the last arc, the two arcs will join
correctly. By specifying one axis to be zero, a horizontal or vertical line
can be drawn. Angles are computed based solely on the coordinate system
and ignore the aspect ratio.

All x and y members are signed integers. The width and height members are
16-bit unsigned integers. You should be careful not to generate coordinates
and sizes out of the 16-bit ranges, because the protocol only has 16-bit
fields for these values.